The invention relates to the operation of an electromagnetic servo mechanism according to the preamble of claim 1. It relates especially to a servo mechanism for operating an internal combustion engine.
A known servo mechanism (DE 195 26 683 A1) has a correcting element in the form of a gas reversal valve, and a servo driver. The servo driver has two electromagnets between which an armature plate can be moved against the force of a restoring means by shutting off the coil current at the holding electromagnet and turning on the coil current at the capturing electromagnet. The coil current of the capturing electromagnet is kept constant at a given capture current during a given period of time and is then adjusted by a two-point controller with hysteresis to a holding current until the coil current is shut off.
Manufacturing variations and departures from the given arrangement of the components of the servo driver, especially the restoring means, bring it about that the rest position established by the restoring means is not symmetrical with the contact surfaces on the electromagnets. Thus a strong impact of the armature plate against an electromagnet can occur when the armature plate is driven by the one electromagnet to the other. The impact produces a loud noise.
Ever more stringent legal limits are established for the production of noise by a motor vehicle and the demand for a quietly running internal combustion engine make it essential, if the servo mechanism is to be produced in series, that the noise produced by the servo mechanism be as low as possible.
The invention is addressed to the problem of creating a method for operating a servo mechanism which will reduce the production of noise when an armature plate impacts an electromagnet.
The problem is solved by the features of claim 1. The solution is characterized by the fact that, while the deceleration rate is established as a set value for the current, a deceleration field is produced by the current and generates a force opposed to the acceleration force which acts upon the armature plate. The acceleration force is produced by the tension of the springs. The deceleration force field reduces the impact velocity of the armature plate. The solution moreover has the advantage of reducing wear on the servo driver.
In advantageous embodiments of the invention, the time period T2 depends on the rotational speed and a load factor or on the velocity of the armature plate, or the amount of deceleration depends on the rotational speed and the load factor or the velocity of the armature plate. This makes possible a selective, asymmetrical adjustment of the rest position of the armature plate, without increasing the noise production when the servo mechanism is operated. This is especially desirable if the servo is an exhaust valve, since it has to be opened against the exhaust gas pressure in the cylinder.
Additional advantageous embodiments of the invention are specified in the subordinate claims.